FLOOD02337

• County: Statewide
• Community: State
• Stream Name: South Platte River
• Basin: South Platte
• Title: Geomorphic Assessment at Surveyed Cross-sections South Platte River
• Date: 6/1/1996
• Prepared For: UDFCD
• Prepared By: Michael Stevens
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Cross Section 5

Station 188+95 N. of 144th Ave. (Extended)

East Bank: Between 1986 and 1994, this stratified sand and gravel bank eroded 62 ft
eastward. In 1994, the bank was graded and seeded and the lower part stabilized
with riprap. It has not moved since. The steeper part is now grassed and there
is volunteer grass in the riprap, which terminates a short distance downstream.

West Bank: Stable at this time as the main channel is far to the east side. Up on the
floodplain, there is a tree farm. Downstream, this bank is eroding until the
current reaches the part that was regraded and vegetated and its bottom portion
riprapped three years ago (Spot Photo 10). Prior to that, this bank was rapidly
eroding.

River Bed: Stable, the bed is more than 500 ft wide with only one low-flow gravel bed
channel on the east side. The higher part of the broad expanse of gravel and sand
bar has clumps of trees and a riser (casing) of an abandoned irrigation well, these
being left behind in the middle of the river during a time prior to 1986 when the
river was eroding its banks. Plants and seedlings on the bar were well scoured
by the 1995 runoff; the surface was left with a number of swales. The cross
section is just upsteam from a bend. .

Cross Section 6

Station 223+20 S. of 144th Ave. (Extended)

East Bank: Built up from waste materials from old gravel mining operations and protected
at the base with dumped concrete rubble and some quarry stones. Ten years ago,
the entire bank was covered by dumped concrete slabs. Stable and very straight
for a long ways downstream. Grasses extend even into the rubble. In 1986, there
were only weeds.

West Bank: Serious erosion is beginning as the bend upstream migrates to the west and
downstream. The bank is cohesive silty clay and clear of vegetation. The top
part is vertical and the bottom steeply sloping. On the floodplain, the monument
is near an oil well and tank farm.

River Bed: Stable. Channel is fine gravel with some Urban Veneer. The bars upstream are
gravel and bare. The cross section is oblique to the flow and in a bend.